1.Field of the Invention
The present invention relates to terminal blocks for connecting multiple wire pairs. More particularly, the present invention relates to telecommunications terminal blocks for connecting telephone service wires to telephone company distribution cables.
2. Background of the Prior Art and Related Information
Telecommunications terminal blocks are used to provide electrical connections between telephone customer service wires and the telephone company's distribution cables. Such terminal blocks typically connect from 2 to 50 individual service wire pairs to the distribution cable which may have several thousand wire pairs. The terminal block is spliced to the distribution cable through a splicing cable or stub cable which forms part of the terminal block. The customer service wire pairs in turn are connected to the terminal block through some type of terminal which is easy to connect and reconnect on site.
One of the most commonly used terminals is a simple binding post where a stripped service wire is connected to the binding post and then secured with some type or cap. Another common type of terminal is an insulation displacement terminal where the service wire need not be bared prior to the connection to the terminal block and the insulation is severed through a blade or other sharp surface as the service wire is secured to the terminal. Again, in the insulation displacement type of terminal, some type of cap is typically employed to secure the service wire in place.
While the caps typically employed in the binding post or insulation displacement type terminals provide some protection from the environment, nonetheless, moisture, pollutants, chemicals, dust and even insects may reach the terminal connection resulting in corrosion or other degradation of the contact. This problem is exacerbated by the fact that in addition to the traditional aerial location of such terminal blocks, underground and even underwater terminal block locations are more and more frequently required for telephone distribution applications. Accordingly, efforts have been made to better insulate the terminal in the terminal block from the environment to prevent such degradation. One such approach has been to use a variety of insulating mediums, such as greases or gels to surround the terminal where the electrical connection is made.
One example of the use of an insulating medium to protect a service wire terminal from the environment is illustrated in U.S. Pat. No. 4,734,061 ('061 patent). In the telecommunications terminal block of the '061 patent, the service wire terminals are provided in a number of isolated cells in a terminal block body composed of a dielectric material. A threaded contact plate in the bottom of each cell and a matching threaded plug are used to make the electrical connection with the service wire. An O-ring seal is provided on the plug to contact the wall of the cell as the plug is inserted into the cell to reduce moisture and other environmental hazards entering into the contact area. Additionally, an insulation medium such as a silicon gel is injected into the region below the plug during manufacture of the terminal block to provide further protection from the environment.
Although the terminal block of the '061 patent apparently provides improved environmental protection over a simple screw type binding post terminal, nonetheless, the entry of moisture or other environmental hazards through the service wire entry openings into the cells is only prevented by the presence of an insulating gel in the contact area of the cell and by precise matching of the service wire diameter to the wire entrance holes. Due to the requirement that the plug make secure contact with the service wire in the bottom of the cell, however, the volume in the cell available for an insulating gel is very limited. During repeated connections and reconnections of service wires inserted into the gel containing portion of the cell, this gel may be lost or displaced, leaving room for moisture or environmental contaminants to enter into the electrical contact area within the cell. Furthermore, such approach is not readily adaptable to an insulation piercing type of terminal since such a terminal requires the service wires to be displaced a sufficient distance in the cell to have the insulation cut by an insulation cutting blade. During such a relatively large displacement, gel would be forced out of the service wire openings and lost, permitting moisture or other contaminants to enter the cell when a reconnection is made.
Another approach to overcoming the problem of protecting contact terminals from the environment is illustrated in U.S. Pat. No. 4,846,721 ('721 patent). In the telecommunications terminal block of the '721 patent, a threaded binding post and matching threaded cap are employed to make electrical contact to a service wire inserted into an aperture in the terminal block body. Additionally, in the '721 patent, provision is made for employing increased amounts of insulating gel in the aperture by providing another aperture for overflow gel to flow into as the binding cap is screwed down onto the binding post. Although this approach allows use of an increased volume of gel, and apparently is directed to overcoming some of the problems discussed above in relation to the '061 patent, nonetheless, such approach is believed to introduce problems of its own. In particular, the gel overflow aperture would itself provide an access point for moisture or contaminants if left open to the outside of the terminal block body. Alternatively, if the aperture is closed then the volume of gel would be limited due to the compression resulting from driving the gel into the aperture during screwing down of the cap. Additionally, during repeated connections and reconnections of service wires, voids could be introduced into the region surrounding the connection due to gel flowing into and out of the aperture during repeated screwing and unscrewing of the binding cap.
Accordingly, a need presently exists for an improved telecommunications terminal block having increased resistance to moisture and other environmental factors which subject the connections therein to degradation over time and limit the applications where such terminal blocks may be reliably employed.